1. Field of the Invention
The invention relates to an advanced formulation scale conditioning process and composition for enhancing the removal or structural modification of films, scales, and sludge deposits from industrial process vessels and piping, such as shell and tube heat exchangers, boilers, and steam generators. In particular, the present invention relates to an advanced formulation scale conditioning process and composition for either enhancing the removal of films, scales, sludge deposits and the like, or modifying their structure, that can be performed at a wide range of pH levels and increased concentration levels. The composition has been shown to increase the porosity of the deposits to aid in their removal or enhance heat transfer through the deposits during heat exchanger operation. The composition does not adversely effect the structural integrity of the heat exchanger. As such, the duration of the cleaning process can be increased which further promotes increase in the porosity of the films, scales and sludge deposits.
2. Related Art
Metal surfaces exposed to water or aqueous solutions over long periods of time in closed heat transfer systems develop scales and/or become covered by sludge and other deposits. This occurs regardless of the system water purity levels. For example, in commercial electric power generating plants, after on-line operation at temperatures of 200° C. or more, large shell and tube heat exchangers, such as those known as nuclear steam generators, develop adherent scales and/or sludge deposits on the secondary side surfaces of tubes, tube sheets, tube support plates, and other internal structural parts. These troublesome scales and deposits form even in those instances in which the purity of the water may be controlled to levels at or below parts per million or parts per billion. Over a period of time, the accumulation of these scales and sludge will have an adverse effect on the operational performance of the steam generators.
Various off-line cleaning methods have been developed to remove the scales and sludge built up on the internal surfaces of heat exchangers used to generate steam. Commercially successful methods include: pressure pulsing with shock waves; water slapping; chemical cleaning at elevated temperatures, using a variety of chelants at concentrations ranging between approximately 5 and 25%; use of scale conditioning agents at elevated pH (around 10.5); and flushing with high pressure water. Both pressure pulse and chemical methods for cleaning the interior of heat exchanger vessels such as the secondary sides of nuclear steam generators are known in the prior art. U.S. Pat. No. 4,899,697 to Franklin et al., U.S. Pat. No. 4,921,662 to Franklin et al., U.S. Pat. No. 5,006,304 to Franklin et al., U.S. Pat. No. 5,092,280 to Franklin, et al., and U.S. Pat. No. 5,092,355 to Cadwell et al. all disclose pressure pulse cleaning methods and devices to loosen and remove sludge and debris from heat exchanger surfaces within the secondary side of nuclear steam generators by means of shock waves introduced in water. U.S. Pat. No. 5,019,329 to Franklin et al. discloses an improved cleaning method for the secondary side of nuclear steam generators by means of vertically flushing the secondary side of nuclear steam generators during pressure pulse or other shock wave type cleaning operations.
In prior art chemical cleaning processes, it was typically necessary to introduce and remove chemical cleaning agents and rinsing solutions a number of times before the sludge and deposits have been effectively removed. In such prior art processes, it was also typically necessary to heat the system during the cleaning process to achieve satisfactory results. Also, in the prior art many of the cleaning agents employed were corrosive and both promoted new and unwanted corrosion of carbon and low alloy steels and/or required an additional neutralization or rinsing step. In some prior art methods, using corrosion inhibitors could decrease this corrosion. However, the inclusion of corrosion inhibitors imposes additional limits, or constraints, on the application temperature of the cleaning process, since these corrosion inhibitors have diminished effectiveness and/or can undergo thermal decomposition as the temperature of the cleaning operation exceeds 120° C.
U.S. Pat. No. 5,764,717 to Rootham and U.S. Pat. No. 5,841,826 to Rootham et al. disclose chemical cleaning methods for removing scale sludge and other deposits from nuclear steam generators. Pressure pulses are generated in a non-corrosive basic amine-containing chemical cleaning agent in aqueous solution after a cleaning agent is introduced into the interior of the generator. The chemical cleaning agents are passive towards ferritic materials. In particular, these scale conditioning agent formulations were designed to minimize interaction with magnetite, the principal component of most scale and hardened sludge deposits. It is believed that minimizing interaction with these materials would eliminate any corrosive effects in the interior of the secondary side of the generator.
U.S. Pat. No. 5,779,814 to Fellers et al. and U.S. Pat. No. 6,017,399 to Fellers et al. disclose a method for controlling and removing solid deposits from components in a steam generating system. The method includes adding a volatile amine to an aqueous phase in the steam generating system. The aqueous phase containing the volatile amine is then converted to steam and brought into contact with the compound in the system containing the solid deposits.